Variable resistor



Sept, 27, 1960 E. .BLANCO 2,954,539

VARIABLE REsIsToR Filed May 27, 1957 IN VEN TOR.

Patented Sept. 27, 1960 2,954,539 VARIABLE REslsToR Elias Blanco, LosAngeles, Calif., assignor, by mesne assignments, to Daystrom,Incorporated, Murray Hill, NJ., a corporation of New Jersey Filed May27, 1957, Ser. No. 661,790

4 Claims. (Cl. 3'387) The present invention relates generally tovariable resistors or potentiometers, and is more particularly concernedwith devices of this type which may be built in miniature or extremelysmall size, and yet have stable characteristics under relatively extremechanges in operating conditions.

It is one object of the herein described invention to provide a variableresistor which will have a high degree of accuracy, and which willretain its stability under extreme temperature variations.

A further object of the invention is to provide a variable resistorwherein the resistor and wiper mechanism are associated and supported insuch a way that inaccuracies due to strain gauge effect will beeliminated.

A further object is to provide in a miniature or extremely small sizeresistor of the character considered herein, a unique clutch between thewiper contact and its actuating mechanism.

A still further object is to provide a unitary clutch and wiper assemblywhich may be constructed from a flat sheet of material. v Another objectof the invention is to provide a unique wiper having a double contactconstruction for engaging diametrically opposite sides of the resistanceelement, so as to provide increased stability under accelerationconditions and during periods of vibration such as might be met with inaircraft or in guided missiles.

Still another object is to provide in such resistors an improvedmanually adjustable element adapted to receive an adjusting tool such asa screw driver, and wherein the tool will be retained againstinadvertent displacement while making adjustments.

Further objects of the invention will be brought out in the followingpart of the specication, wherein detailed description is for the purposeof `fully disclosing the invention without placing limitations thereon.

Referring to the accompanying drawings, which are for illustrativepurposes only:

Fig. l is a perspective view of a variable resistor embodying thefeatures of the present invention;

Fig. 2 is a transverse section taken substantially on line 2 2 of Fig.1;

Fig. 3 is a longitudinal section taken substantially on line 3 3 of Fig.2, certain parts being shown in elevation to clarify the cooperativerelationship;

Fig. 4 is an end elevational view showing means for manually adjustingthe resistor;

Fig. 5 is an enlarged side elevational view of the wiper assembly; and

Fig. 6 is an end view of the same.

Referring more specically to the drawings, for illustrative purposes,the variable resistor is shown in Fig. 1 as being housed Within a hollowboxlike structure, as generally indicated at 10. This structure forms acasing for the component parts of the resistor and maybe constructed ofmolded plastic or fabricated from other suitable insulating material.The casing is constructed with an integrally formed end wall 11 at oneend, while the other end is open ended, this latter end being closed bymeans of an end wall `12 which forms a terminal-block and is removablysecured in a position closing this end of the structure by suitableretaining screws k13 and 14.

A resistance element 15 is supported within the casing, the resistanceelement comprising a iine resistance wire without insulation which iscoiled around an insulated outer surface 17 of an elongate mandrel 18.The ends of this mandrel are supported in sockets 19 and 20 respectivelyformed in the end walls 1:1 and I12,. These sockets support the mandrelat its ends and retain the resistance element against lateraldisplacement within a main compartment 21, and out of contact with thesurrounding compartment wall. The mandrel, however, is preloaded in anaxial direction by means of spring washers 22 positioned within thesocket 19 between the adjacent end of the mandrel and the bottom of thesocket so as to resiliently bias the mandrel in a direction to cause itsopposite end to forceably abut and bear against the bottom of the socket20.

As shown in Figs. 2 and 3, an elongate screw 23 extends along side theresistance element, this screw and resistance element having theirlongitudinal axes in parallel relation. The screw 23 extends through anauxiliary channel 24 formed in the structure 10 and having parallelspaced side walls 25 and 26.

One end of the screw 23 is formed with an extension 27 having its endsurface rounded as indicated at 28. This end is seated within a socket29 vformed in the head portion of a pickoff which thus rotatablysupports this end of the screw and also serves as a terminal connectortherewith.

The other end of the screw 23 is formed with an end extension 31 whichis positioned at its outer end in a socket 32 of a coupler 33 supportedin the end wall 1|1 for rotational movement. The end extension 31 andcoupler 33 have overlapped surfaces 34 and 35 which interlock these twoelements together for unitary rotational movement yet permit slightrelative axial movements therebetween. As in the case of the mandrel 18,the screw 23 is likewise preloaded. For this purpose, a coiledcompression spring 36 is kpositioned around the end extension 31, oneend of this spring bearing against an abutment washer 3'7 carried bythescrew 23, and the other end of this spring bearing against theadjacent end of the coupler 33. The action of this spring is to forceanA abutment shoulder 38 on the coupler 33 against a shoulder 39 formedin the end wall 11. At the same time, the spring biases the screw 23 ina direction to retain the extension 27 in pressure seated position inthe socket 29.

The outermost end of the coupler 33 carries a cap member 39 whichprojects outwardly from the end face of the end wall 11 and providesmeans by which the screw 23 may be rotated to move associated resistancewiper means `40 therealong. The projecting end of the cap 39, as shownin Fig. 4, is provided with a transversely extending slot 41 for thereception of a suitable adjusting tool such as a screw driver. Themaking of adjustments is further facilitated by providing a recessedbottom portion `42 between the ends of the slot 41, whereby spacedabutment surfaces 43 and `44 are formed adjacent and inwardly spacedfrom the respective ends of the slot 41. The adjusting screw driver maybe inserted within the recessed bottom portion 42 and will be heldagainst axial displacement via the ends of the slot by the abutmentsurfaces 43 and l44.

The wiper means 40 is of unique construction in that it may befabricated from a at sheet of resilient material having good electricalconducting characteristics. The blank is deformed to provide a tubularportion 45, Figs. 5 and 6, which surrounds the threads of the screw 23and is slidable therealong. Integrally formed arms 46 and 47 extend fromthe opposite ends of a diameter of the tubular portion. These armsrespectively have tangentially extending portions 48 and 49 which are inparallel relation and connect with outwardly offset portions 50 and 51.As shown in Fig. 2, the portions 4S and 49 extend into the auxiliarychannel 24 and cooperate with the side walls 25 and 26 thereof to retainthe tubular portion against rotation with the screw 23, while theportions 50 and 51 are respectively disposed on diametrically oppositesides of the mandrel 13 and form contacts resiliently engaging with theresistance wire 16. With this construction, the wiper means andresistance Wire engaging contacts are effectively stabilized againstdisplacement due to vibrations etc.

The wiper means has a unique clutch connection with the threads of thescrew 23. The opposite ends of the tubular portion 45 is fabricated withoppositely extending resilient curved arms 52 and 5'3 which conformgenerally to the curvature of the tubular portion 45. The outermost endof the arms 52 and 53 are respectively deformed to provide inwardlyextending projections 54 and 5S which are arranged to be normallypositioned between adjacent threads of the screw 23. With thisarrangement, under normal conditions rotation of the screw will causethe wiper means to be axially moved along the screw and carry thecontacts 50 and 51 into engagement with successive turns of theresistance wire. However, when the limits of travel of the wiper meanstakes place, the tubular portion will abut the end wall 11 or end wall12, as the case may be. At these limit positions, further attempt tomove the wiper means in a direction of the abutment by rotating thescrew y23 will cause the threads to act with a cam action against theprojections S4 and 55, exing the arms 52 and 53 so as to disengage theseprojections from the threads. Movement of the screw 23 in a direction tomotivate the wiper means away from the abutment will permit 'theprojections to function in normal manner for movement of the wipermeans.

Connections are made to the device by means of conductors 56, 57 and 58,as shown in Fig. 1, these conductors being carried through passagesformed in the end wall 12. As shown in Fig. 3, the conductor 56 isconnected with the picko terminal so that an electrical path isestablished through the pickoft, the screw 23 and the wiper means to thecoil turns of the resistance wire 16 wound on the mandrel 18.

The wire 57 is shown as being connected to one end of the mandrel 18which serves as a conductor for completing an electrical path from thisconductor through the mandrel which is connected through a soldered orotherwise formed connection 59 between one end of the resistance wireand the mandrel. The conductor 58 is shown as being connected through asoldered or otherwise formed connection 60 by which an electrical ilowpath is established with the other end of the resistance wlre.

Further stability is obtained due to the loading elect of the springs 22and 36 on the mandrel 18 and screw 23 respectively, and since theseelements are supported at their ends, the material constituting theelements is free to expand and contract under temperature variations.Since there are no adhesives or other anchoring means utilized along themandrel or screw, objectionable strain gauge effects and errorsresulting therefrom will be avoided.

Moreover, it should be pointed out that the bottom surface of the socket20, as indicated by the numeral 61, is substantially in the sametransverse plane as the surface 28. By constructing the mandrel 18 andthe screw 23 of materials having substantially the same coefcient ofexpansion, variations of the mandrel and screw with respect to thereference plane of the surfaces 61 and 28 will be of the same order, andrelative movement be- -tween the screw and mandrel due to temperaturechanges 4 will be susbtantially eliminated so that greater accuracy willbe obtained and the device wi-ll be stable under widely varyingtemperatureconditions. Copper alloys have been successfully utilized forthe construction material for the mandrel and the screw.

In some installations, it is desirable that the variable resistors ofthe type disclosed herein be arranged for mounting in stacked superposedrelation. In the present instance, the ends walls 11 and 12 are providedwith holes 62 for receiving posts (not shown) upon which the resistorsmay be stacked and secured in superposed relation.

Various modifications may suggest themselves to those skilled in the artwithout departing from the spirit of my invention, and, hence, I do notwish to be restricted to the specific form shown or uses mentionedexcept to the extent indicated in the appended claims.

I claim:

1. A variable resistor, comprising: a support; a mandrel; a resistanceelement carried by said mandrel; an elongate screw, said screw andmandrel each having one end restrained in said support against axialmovement in one direction; resilient loading means associated with theyother ends of said screw and mandrel appl-ying pressure thereto in saidone direction, but permitting corresponding expansion and contract-ionof said screw and mandrel with respect to said support at said one endin response to ambient temperature changes; and movable w-iper meansactuated by said screw hav-ing Contact with said resistance element,said mandrel and screw being constructed of materials havingsubstantially the same coefficient of expansion.

2. A variable resistor, comprising: a support; a mandrel; a resistanceelement carried by said mandrel; an elongate screw extending along oneside of said mandrel, said screw and mandrel having substantially thesame coefticient of expansion; abutment surfaces carried by said supportproviding points of abutting engagement yfor the adjacent ends of saidscrew and said mandrel, said points off engagement lying substantiallyin a common plane at right angles to the longitudinal axis of said screwand mandrel; movable wiper means actuated by said screw having contactwith said resistance element; and spring means associated with the otherends of said screw and mandrel for applying a load biasing pressurethereon in a direction towards said abutment surfaces, lwhereby saidscrew and mandrel are free to expand and contract together withoutdisturbing the wiper setting relative to said resist-ance element.

3. A variable resistor, comprising: a housing defining an elongate maincompartment extending between end walls; an elongate mandrel having itsends respectively supported in said end walls; a resistance elementcarried by said mandrel; an auxiliary channel extending between said endwalls, said channel having spaced side walls on opposite sides of anelongate opening facing said resistlance element; a screw in saidchannel having its ends rotatably supported in said end walls, saidscrew being rotatable from the exterior of one of said end walls; andwiper means carried by said screw including a pair of arms having outerends resiliently contacting said resistance element on opposite sides ofsaid mandrel, and inner end portions respectively lying in closeproximity to said side walls, whereby said 'wiper means are stabilizedlaterally.

4. A variable resistor, comprising: a housing dening an elongated maincompartment extending between end walls; an elongate mandrel having itsends respectively supported in said end walls and retained at one ofsaid end walls against axial movement in a direction towards the same; aresistance element carried by said mandrel; an auxiliary channelextending between said end walls, said channel having spaced side wallson opposite sides of an elongate opening facing said resistance element;

a screw in said channel having its ends rotatably supported in said endwalls and retained at said one of said end walls against axial movementin a direction towards the same, said screw and mandrel beingconstructed of materials having substantially similar coeicients ofexpansion; means at the other of said end walls spring loading saidscrew and mandrel in an axial direction towards said one of said endwalls; means for rotating said screw from the exterior of said housing;and wiper means carried by said screw including a pair of arms havingouter ends resiliently contacting said resistance element on oppositesides of said mandrel, and inner end portions respectively lying inclose proximity to said side walls, whereby said wiper means arelaterally stabilized.

UNITED STATES PATENTS Schowe Aug. 5, 1879 Leyenberger May 8, 1956 BournsJan. 15, 1957 Laisy May 6, 1958 FOREIGN PATENTS Great Britain May 28,1947 Great Brtiain Mar. 12, 1952 Canada Oot. 18, 1949 Germany Nov. 19,1951 Switzerland May 16, 1946

